Molybdenite (molybdenum disulfide, MoS.sub.2) is the most important source of the metal, molybdenum. The mineral occurs, usually, in low concentration along with other metal sulfide minerals such as those of iron and copper. Vexing problems have arisen in working up ores containing molybdenite since in many cases, the primary metal value sought to be recovered is another base metal such as copper, with the molybdenite content being so low that, in many cases, it is regarded as a byproduct. Known molybdenite flotation practices can be classified into two major classes; namely: (1) selective flotation of molybdenite and (2) bulk sulfide flotation. Selective flotation is generally used by primary producers of molybdenum and is generally applied in cases where molybdenite is the primary mineral of interest in the ore being treated while bulk sulfide flotation is generally employed in byproduct or coproduct recovery of molybdenite in conjunction, usually, with primary copper recovery.
As implied by the names, selective flotation involves floating molybdenite selectively from the ground ore while other sulfide minerals and gangue ore are depressed in the same step. The grind employed may be relatively coarse, e.g., 35% to 40% plus 100 mesh, the reagent suite required is complex and expensive, the process is not suited to recovery of byproducts and/or coproducts but product quality is excellent. Reagents employed include collectors such as a refined petroleum oil ("vapor oil" or diesel oil), frothers or conditioners such as syntex (sulfated glyceride of coconut oil), pine oil, depressers such as sodium silicate, sodium cyanide or Nokes reagent (see U.S. Pat. No. 2,492,936).
Bulk sulfide flotation involves floating all the sulfides contained in the ore to produce a bulk concentrate which must then be treated further to separate molybdenite from other sulfide values such as copper. This is usually done in a flotation operation in which the sulfides of copper and other metals present are depressed and the molybdenite is floated with a collector, e.g., an oil. The molybdenite is further cleaned to produce a commercial grade concentrate while the tailing is further treated by flotation to produce concentrates of copper and other co-present values. Usually a fine grind is required, e.g., 15 to 20% plus 100 mesh, and multistage flotation circuits are required. Concentrate grade tends to be lower and leaching may be required to remove lead, copper or iron to produce a marketable-grade product.
It should also be mentioned that when an oil is used as a collector for molybdenite, the resulting concentrate will contain substantial quantities of oil, e.g., up to as much as 10% by weight. Such quantities of oil cause problems in many downstream operations such as roasting. Thus, even though oil may be used in quite small amounts based upon weight of ore treated, these amounts of oil are still substantial in terms of molybdenite content of the ore, which may be, for example, only 0.3% by weight, or much less.
Those skilled in the art are aware that once a mineral surface has been treated to depress the mineral using a depressing agent, the effect of the depressing agent must be overcome before the mineral can be floated successfully in later flotation operation. Many means for accomplishing this have been suggested in the art, but all involve multiple treatments and many suggest complex flotation circuits and use of many different reagents for different purposes. Patents dealing with the problems discussed include U.S. Pat. Nos. 2,559,104; 2,608,298; 2,664,199; 2,811,255; 2,957,576; 3,102,854; 3,313,412; 3,329,266; 3,375,924; 3,400,817; 3,435,952, 3,539,002. U.S. Pat. No. 3,082,065 deals with the problem of grinding wet, oily molybdenite concentrate to produce a dry lubricant using a fluid energy reduction mill.
The process of the present invention addresses the problem of providing an improved process for treating a molybdenite ore to provide an increased yield of molybdenite suitable for lubricant purposes, reduce reagent costs and facilitate recovery of byproducts from the ore.